This invention relates to a vehicle headlamp control system having a control circuit which is able to control the intensities of illumination of headlamps which are suitable for vehicles traveling in countries such as those in Northern Europe or Canada where there are white nights, or in countries where it is often misty.
In countries high in altitude such as those in the Northern Europe and Canada, there is a white night season in which it is dim. In England, it is frequently foggy, and sometimes it is required to turn on vehicle headlamps even in daytime. In those countries, it is necessary to turn on vehicle headlamps for traffic safety even in daytime, and it is obliged by law to do so.
In compliance with the law, in addition to the headlamps, auxiliary headlamps lower in illuminance than them are mounted on the vehicle, or a control system is provided for the headlamps. The control system, as described below in detail, has a current limiting resistor for limiting the currents applied to the headlamps thereby limiting the intensities of illumination of the latter.
FIG. 7 is a circuit diagram showing an example of a conventional vehicle headlamp control system.
In FIG. 7, reference characters 1.sub.R and 1.sub.L designate right and left headlamps; 2, an alternator; 3, a parking brake switch; 4, a current limiting resistor; 5, a dimmer passing switch; 6, a headlamp switch; 7, a battery; and 8 through 12, relays.
In the control system, the limiting resistor 4 limits the currents supplied to the headlamps 1.sub.R and 1.sub.L thereby lowering the intensities of illumination of the latter.
The control system operates as follows:
When the vehicle is parked, the alternator 2 produces no charge signal (i.e., an engine start signal), and therefore no current is applied to the exciting coils 11.sub.1, 12.sub.1 and 9.sub.1 of the relays 11, 12 and 9, and the headlamps 1.sub.R and 1.sub.L are kept turned off.
When the engine starts; that is, when the alternator 2 rotates to produce the charge signal, current is supplied to the exciting coils 11.sub.1 and 12.sub.1 of the relays 11 and 12, so that the relays 11 and 12 are activated. As a result, the contact means 12.sub.a of the relay 12 is opened, while the contact means 12.sub.b is closed, so that the battery 7 is connected through the contact means 12.sub.b to the headlamps 1.sub.R and 1.sub.L. At the same time, the contact means of the relay 11 is connected through a contact 11.sub.b to the current limiting resistor 4, so that the low beam elements L.sub.o of the headlamps 1.sub.R and 1.sub.L are grounded through the limiting resistor 4; that is, the intensities illumination of the headlamps 1.sub.R and 1.sub.L are decreased.
When the headlamp switch 6 is turned on, current is applied to the exciting coil 9.sub.1 of the relay 9, so that its contact means 9.sub.a is opened to interrupt the application of current to the relays 11 and 12. At the same time, the contact means 9.sub.b of the relay 9 is closed, so that the battery 7 is electrically connected through the contact means 8.sub.a of the relay 8 to first terminals of the low beam elements L.sub.o of the headlamps 1.sub.R and 1.sub.L, the remaining second terminals of which are grounded through the contact means 11.sub.a of the relay 11 and through a contact 5.sub.a of first contact means of the dimmer passing switch 5, as a result of which the low beam elements of the headlamps 1.sub.R and 1.sub.L are turned on. On the other hand, when the passing switch 5 is operated, the armature of the first contact means is tripped over to the contact 5.sub.b from the contact 5.sub.a, so that the high beam elements H.sub. i of the headlamps 1.sub.R and 1.sub.L are turned on.
When the parking brake switch 3 is turned on, the relay 10 is activated; that is, the armature of its contact means is tripped over to a contact 10b, so that the contact means of the relays 11, 12 and 9 are restored (placed in the initial states); that is, the headlamps 1.sub.R and 1.sub.L are turned off.
In the conventional vehicle headlamp control system, sequential control is performed by using the relays, to control the operations of the headlamps 1.sub.R and 1.sub.L. In order to control the headlamps 1.sub.R and 1.sub.L accurately, it is necessary to provide a control circuit intricate in arrangement. On the other hand, controlling the illuminance is achieved by using the current limiting resistor; that is, the current limiting resistor adjusts the current flowing to the headlamps 1.sub.R and 1.sub.L thereby to adjust the intensities of illumination of the latter. In the above-described relay-operated sequential control, it is considerably difficult to supply pulse currents through the relays, and it is impossible to adjust the duty ratios of the pulse currents applied to the headlamps 1.sub.R and 1.sub.L.
Furthermore, different countries employ different headlamp specifications, and different headlamps have different requirements in design. Hence, the aforementioned relay-operated sequential control by the control circuit in the vehicle headlamp control system is not sufficient for timing control. The intensities of illumination of the headlamps may be adjusted by changing the resistance of the current limiting resistor. However, in this case, it is necessary to select the resistance so as to obtain the aimed intensities illumination. This selection is rather troublesome. Thus, the conventional relay-operated sequential control system cannot sufficiently deal with various controls for the headlamps.